Generally, with reference to FIG. 11, a rotation detection device is used to detect a rotation of an object such as a vehicle-mounted engine and a vehicle wheel (for wheel velocity detection) and the like, for example, as disclosed in JP-7-260813A (U.S. Pat. No. 5,637,995).
As shown in FIG. 11, the rotation detection device has a sensor chip 101 (magnetism detection unit) which is arranged to face a rotor RT as the detection object. The sensor chip 101 has a magnetic resistance element pair 1 including a magnetic resistance element MRE1 and a magnetic resistance element MRE2, and a magnetic resistance element pair 2 including a magnetic resistance element MRE3 and a magnetic resistance element MRE4. The sensor chip 101 and a processing circuit thereof are arranged in an integrated circuit, and integrally molded in a mold resin 102.
Specifically, the sensor chip 101 is mounted to one end of a lead frame (not shown) in the mold resin 102. A feeding terminal T1, an output terminal T2, and a GND (grounding) terminal T3 are arranged at other end of the lead frame to be respectively connected to the exterior.
Moreover, a magnet 30 (bias magnet) is arranged in the vicinity of the sensor chip 101 to surround the mold resin 102. The magnet 30 applies a bias magnetic field to the magnetic resistance element pairs 1 and 2. The magnet 30 which has a hollow cylinder shape is provided with a hollow portion 31 extending in the longitudinal direction of the magnet 30. The mold resin 102 in which the sensor chip 101 is embraced is inserted in the hollow portion 31.
In the practical use of the rotation detection device, the mold resin 102 in which the sensor chip 101 is molded, and the magnet 30, and the like are accommodated in a suitable case member. The whole of the rotation detection device which has been cased is mounted to an engine or the like, with reference to FIG. 12. The component shown FIG. 12 and that shown in FIG. 11 which have the same function are same numbered.
As shown in FIG. 12, the mold resin 102 and the magnet 30 are integrated with a housing resin 120 (sensor body member), in such a manner that the mold resin 102 and the magnet 30 are accommodated in a cap member 40 (cover member) which is bottomed. The housing resin 120 has a flange 123 used for a connection with an engine body or the like, and a connector portion 124 which extends from the flange 123 and functions as a connector for a connection with an electronic control device or the like of the exterior through wirings. The terminals T1-T3 are respectively electrically connected with metal terminals 100a-100c which are integrally arranged in the housing resin 120 and also used as terminals of the connector portion 124.
The rotor RT which faces the sensor chip 101 can be constructed of a magnetic member having a gear shape, for example. With a rotation of the rotor RT, there is a variation in a magnetic vector which is resultant due to the magnetic field generated by the rotator RT and that generated by the magnet 30. The sensor chip 101 detects the vibration in the magnetic vector as a variation in a resistance value of the magnetic resistance element. Thus, a rotation detection signal can be obtained.
Then, the rotation information of the rotator RT is transferred to the exterior electronic control device (not shown) or the like through the output terminal T2, after passing various process circuits such as a differential amplifier, and a comparator and the like.
However, in this case, the mold resin 102 where the sensor chip 101 is embraced, the magnet 30 and the cap member 40 are respectively constructed of primary-molding members by injection molding. These primary-molding members are sequentially assembled in the order of the mold resin 102, the magnet 30 and the cap member 40, and then set in a suitable mold. Thereafter, the housing resin 120 is constructed by injection molding to be arranged around the mold resin 102, the magnet 30 and the cap member 40. That is, the housing resin 120 is formed as a secondary-molding member, so that the sensor body member is integrated.
Therefore, the sensor chip 101 (of rotation detection device) where the magnetic resistance element pairs are arranged is isolated from ambient air of the exterior and protected from pollution and the like, by the mold resin 102.
However, when the sensor chip 101 is molded in the mold resin 102, the interior stress is directly applied to the sensor chip 101. In the shipment, a suitability is sought by obtaining an appropriate detection output in this state. In this case, the variation in the sensing property due to the time-varying interior stress cannot be ignored.
That is, after the shipment of the rotation detection device to the market and the mounting of the rotation detection device to a vehicle-mounted engine or a general machine, the interior stress which is applied to the sensor chip 101 has a tendency to be gradually released due to an environment change such as a temperature stress and the like.
Due to the release of the interior stress, an offset variation will be caused because of a magnetostriction effect. Thus, it is difficult to avoid the influence of the offset variation on the sensing property of the rotation detection device.
Recently, it is proposed that the sensor chip 101 in a bare-chip state is mounted to the sensor body member 120 and both the sensor chip 101 and the magnet 30 are covered by the cap member 40. In this case, the cap member 40 is bottomed, and the opening end of the cap member 40 is joined to the sensor body member 120.
On the other hand, with the miniaturization of various sensor members, the miniaturization of the rotation detection device is desirable. Specially, it is desirable to shorten a distance from a mounting surface (to vehicle-mounted engine or the like) to an end surface of the rotation detection device, that is, a distance UL (i.e., under-neck length) from the mounting surface of the flange 123 of the rotation detection device (shown in FIG. 12) to the outer surface of the end portion of the cap member 40.
Because the detection sensitivity of the rotation detection device greatly depends on the distance between the end surface of the rotation detection device and the detection object (e.g., rotor RT), it is important to set the distance UL which corresponds to a distance of the inner side of the mounting surface of the flange 40. Practically, in addition to shorten the distance UL, it is also desirable to provide the rotation detection devices having various sizes corresponding to the machines to which the rotation detection devices are to be mounted.
However, in the case where the sensor chip in the state of the bare chip is mounted to the sensor body member 120, the following problems cannot be ignored. That is, though the joining area between the sensor body member 120 and the cap member 40 can be maintained in the case where the rotation detection device is provided with the long distance UL, it is difficult to maintain the joining area in the case where the rotation detection device is provided with the short distance UL.
Thus, it is difficult to sufficiently maintain the joining area between the sensor body member 120 and the cap member 40. In the case where the hermeticity of the joining portion cannot be maintained due to the vibration or the like of the object to which the rotation detection device is mounted, the isolation of the sensor chip 101 (mounted in bare chip state) from the ambient air is deteriorated.